Stringer of water sports board with enhanced flexibility and water sports board containing 
thereof

ABSTRACT

A water sports board having enhanced flexibility includes an elongated core body having a nose end and a tail end, and top and bottom surfaces defining a curved shape of the water sports board; and an elongated planar stringer disposed on a longitudinal centerline of the core body. The elongated planar stringer has a front end and a rear end, two side surfaces, and top and bottom edges curved to a longitudinal profile of the water sports board, and includes multiple slots on the side surfaces disposed between the front and rear ends of the stringer. The flex pattern of the water sports board can be controlled by selecting desired number, size, shape, and location of the slots of the stringer. The water sports board has an increased rocker and enhanced shock dampening property when exposed to the force of water waves.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 USC 119 (e) of the provisional patent application Ser. No. 61/051,418, filed May 8, 2008, which is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to water sports boards and stringers used therein. More particularly, the present invention provides water sports boards including a slotted stringer with enhanced flexibility.

BACKGROUND OF THE INVENTION

Board-shaped riding vehicles have long been a part of water recreation, first as surfboards, and later as sail boards and body boards. Surfboards were traditionally stiff and heavy, with hard exterior surfaces. In recent years, surf and sail board manufacturers have utilized synthetic materials to make light weight boards, and body boards are normally constructed from soft foam materials.

Currently available surfboards generally have light density core material glued to a wood stringer positioned at a longitudinal centerline and covered by a hard exterior skin layer. The purpose of a stringer is to provide structural strength to the surfboard. As can be appreciated, the flexibility of the stringer directly affects the flexibility of the surfboard. Surfboard is required to flex a desired amount and at desired locations. Almost all commercially available surfboards have one, or sometimes two, thin planar wood stringer, because of its more desirable flexibility. However, the flex patterns and characteristics exhibited by existing surfboards are random, not pre-determined and less than optimal. This is mainly due to the random flex characteristics and resistance to flexing of the solid body stringer. Moreover, the material types and the width of the stringers also play a role in the random and uncontrolled flex characteristics. Because of limited flexibility, existing surfboards tend to break easily under harsh wave conditions or repetitive uses.

Therefore, it is desirable to provide a water sports board having an improved flexibility. It is further desirable to provide a water sports board with selected or predetermined desired flex patterns, which ultimately enhances maneuverability and performance of the board to the rider. Moreover, it is also desirable to provide water sports boards with improved shock dampening property to enhance durability of the boards particularly in extreme environments.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to a water sports board having enhanced flexibility. The water sports board comprises an elongated core body having a nose end and a tail end, and top and bottom surfaces defining a curved shape of the water sports board; and an elongated planar stringer having a front end and a rear end, two side surfaces, and top and bottom edges curved to a longitudinal profile of the water sports board, and including multiple slots on the side surfaces, disposed between the front and rear ends of the stringer. The planar stringer is disposed on a longitudinal centerline of the core body.

In a further embodiment, the present invention is directed to a water sports board that comprises an elongated core body having a nose end and a tail end, and top and bottom surfaces defining a curved shape of the water sports board and two or more elongated planar stringers. Each of the stringers has a front end and a rear end, two side surfaces, and top and bottom edges curved to a longitudinal profile of the water sports board, and includes multiple elongated slots on the side surfaces, each of the elongated slots disposed along a longitudinal axis of the stringer with a predetermined distance from a midpoint of the longitudinal axis. The two or more planar stringers are disposed along, and symmetrically off, a longitudinal centerline of the core body.

In a further embodiment, the present invention is directed to a stringer of a water sports board having enhanced flexibility. The stringer comprises an elongated planar panel having a front end and a rear end, two side surfaces, and top and bottom edges curved to a longitudinal profile of a water sports board, and multiple elongated slots on the side surfaces; each of the multiple elongated slots disposed along a longitudinal axis of the stringer with a predetermined distance from a midpoint of the longitudinal axis.

In a yet further embodiment, the present invention is directed to a method of making a water sports board with the stringer of the present invention.

The advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings showing exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top exterior view of a surfboard containing therein a stringer in one embodiment of the present invention. FIG. 1A is a longitudinal cross-sectional view of the core body of the surfboard of FIG. 1, taken along the longitudinal centerline 2-2′ of the surfboard immediately next to the stringer. FIG. 1B is a front view of the surfboard shown in FIG. 1. FIG. 1C is a perspective view of a cut-off transverse section of the surfboard, taken along line A-A in FIG. 1.

FIG. 2 is an illustrative exploded view of the inner core and the stringer of the surfboard shown in FIG. 1.

FIG. 3 is a side view of a stringer in one embodiment of the present invention.

FIG. 3A is an enlarged perspective view of slot 130C in FIG. 3.

FIG. 4 is an enlarged perspective view of a slot of a stringer in an alternative embodiment of the present invention, where the slot is in a form of recess on the side surface of the stringer.

FIG. 5 is a top view of a blank of a surfboard in a further embodiment, which includes two stringers of the present invention.

FIG. 6 is an illustrative view showing an improved flexibility of the surfboard during its use, as reflected by an increased rocker.

It is noted that in the drawings like numerals refer to like components.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment, the present invention provides a water sports board containing a stringer that has enhanced flexibility. The term “water sports board” used herein includes, but not limited to, surfboards, sail boards or windsurf boards kiteboards, wakeboards, wake skates, and body boards.

Referring to FIGS. 1 thru 3A, in one embodiment, water sports board 10 of the present invention, as illustrated in a form of a surfboard, comprises an elongated core body 20 and an elongated planar stringer 100 positioned on the longitudinal centerline 2-2′ of surfboard 10.

As shown in FIGS. 1 thru FIGS. 1C, elongated core body 20 has a nose end 22 and a tail end 24, and a top surface 26 and a bottom surface 28 defining a curved shape of a surfboard. In the embodiment shown, core body 20 includes an outer shell 30, which covers the entire exterior surface of surfboard 10, and an inner core 40, see FIG. 1C. As shown, the outer shell may often be transparent, stringer 100 is visible from the exterior of the surfboard. It should be understood that core body 20 may also be hollow, with outer shell 30 formed on both sides of the planar stringer 100.

FIG. 2 shows an exploded view of inner core 40 and a stringer 100 of surfboard 10 shown in FIG. 1. In the embodiment shown, inner core 40 includes two symmetrical half cores 40 a and 40 b, both of them have the curved shape or longitudinal profile of surfboard 10. Half cores 40 a and 40 b have nose ends 42 a and 42 b, respectively, and tail ends 44 a and 44 b, respectively. Each half core has a planar inner surface 49 a, or 49 b, as mirror image of each other. The planar inner surfaces are joined to stringer 100 during construction of the surfboard, as described further hereinafter.

As shown in FIGS. 2 and 3, in one embodiment, stringer 100 includes an elongated planar stringer body 110, in a form of a thin panel, which has a front end 112, a rear end 114, a top edge 116, a bottom edge 118, and two opposing side surfaces 122 and 124 extending from front end 112 to rear end 114. The top edge 116 has the same curvature as that of the top surfaces 46 a and 46 b of two half cores 40 a and 40 b, and similarly, bottom edge 118 has the same curvature as that of the bottom surfaces 48 a and 48 b of the two half cores. In other words, top and bottom edges 116 and 118 of stringer body 110 are curved substantially to the longitudinal profile of inner core 40, which defines the longitudinal profile of core body 20. Therefore, the height of the stringer is substantially the same as the height, also referred to as thickness, of the core body.

Stringer 100 includes one or more slots 130, preferably multiple slots, on side surfaces 122, 124, disposed between front end 112 and rear end 114 of the stringer body. FIG. 3 shows one embodiment of stringer 100, which has five slots 130 a to 130 e. Preferably, slot 130 is a through-opening from side surface 122 to side surface 124, completely through the width of stringer body 110, as shown in FIG. 3A. The slots can be fabricated by cutting out portions of the stringer body with selected size, shape and locations, as further described hereinafter, or by molding when a composite or plastic material is used. Each through-opening creates a void within the original solid stringer panel, which provides a certain degree of transient compressibility or deformability to the material of the panel when the stringer is exposed to strong forces of the water waves. In the presence of the slots, stringer 100 has reduced resistance to flexing than the existing solid stringer body made of the same material, such as wood or plywood. A surfboard built with a stringer 100 exhibits a substantially enhanced flexibility and durability, particularly under harsh wave conditions or repetitive uses as further described later.

In an alternative embodiment as shown in FIG. 4, the slot 130′ may also be in a form of recess partially through the width of stringer body 110′. Multiple slots may be arranged on two side surfaces (only 122′ is shown), either at the same location or at different locations along the longitudinal axis. The recess can be formed by partially cutting off the panel material to reduce the width of the stringer body at the slot positions, or by molding when a composite or plastic material is used. The recess can be more suitable when the material itself has a certain level of resilience, as thinning of the material at the slot positions renders the panel less resistant to flexing. Moreover, a combination of through-opening and recess may also be used in one stringer.

Slot 130 can have various shapes, such as elliptical, circular, generally rectangular, narrow linear slit or a combination thereof. Preferably, both front end 132 and rear end 134 of slot 130 have a smooth curvature, or rounded as shown in FIG. 3A. Smooth ends of the slot distribute the forces experienced by the stringer over a wide area of the stringer body and reduce extreme forces encountered at sharp angles, therefore, reduce the possibility of breakage of the stringer.

Preferably, slot 130 is elongated in the direction of the longitudinal axis of stringer 100, as shown in FIGS. 3 and 3A. It is noted that the longitudinal axis of stringer body 110 is generally centered between the top and bottom edges 116 and 118, therefore, for the purpose of describing the present invention the longitudinal axis is curved to the longitudinal profile of the stringer. The elongated slot 130 has an upper edge 136 and a lower edge 138, and rounded front and rear ends 132 and 134. In the embodiment shown, upper and lower edges 136 and 138 are substantially linear; however, the upper and lower edges can also be slightly curved to the curvatures of the corresponding top and bottom edges, respectively, of the stringer body at the location of the slot being disposed, particularly, when the slot is long.

The size and/or shape of the slots can be determined based on the types of water sports boards, locations of slots and desired amount of flex of a board. As can be appreciated, different water sports boards, and their stringers, have different length and thickness. Moreover, as shown in FIGS. 1A and 3, the stringer body and a surfboard have the largest dimension in thickness at the midpoint of the longitudinal axis and smaller dimensions toward the front and rear ends of the stringer body. Therefore, the height, also referred to as gap size, of the elongated slots may vary depending on the thickness or height of a stringer body, and depending on the locations of a slot on the stringer body.

It has been found that in general, when the height of an elongated slot 130 is increased, the amount of flex provided to surfboard 10 is increased by that slot; and when the length of the slot is increased, the area of flex affected by that slot is also, increased, which is distributed over a greater area of surfboard 10 in the longitudinal direction. In contrast, when the height or length of an elongated slot 130 is decreased, the opposite of the above-described effects is observed. On the other hand, it has been found that when the total slotted area, i.e., the total area within all slots of a stringer, increases, the overall flex of a surfboard also increases. Therefore, sometimes, a surfboard having a stringer 100 with a fewer number of longer slots may achieve a desired amount of flex similar to that with more number of relatively shorter slots. Furthermore, optimum size and number of slots also depend on the type or composition of the material of the stringer body and the width of the stringer body. By providing designed slots on the stringer body, the resulting surfboard has characteristics of controlled longitudinal and torsional flexibility.

For shortboards, one type of surfboards, typically having a length from about 3½ feet to about 6½ feet, the elongated slots may have a length from about 2 inches to about 10 inches, preferably from about 3 inches to about 6 inches, and a height from about 1/12 to about 1½ of the height of the stringer body. In one exemplary embodiment, the height of slot 130 can be in a range from about ⅛ inch to about ⅝ inch, preferably, from about ¼ inch to about ½ inch. Moreover, the length of multiple elongated slots within one stringer can be the same or different, depending on the desired flex pattern of a surfboard, or other water sports boards.

As can be appreciated, the desired flexibility should be balanced with the required strength of the stringer. As such, the height of the slots typically does not exceed 75% of the height of the stringer body. Moreover, a total length of the slots is preferably from about 15% to about 60% of the length of the stringer.

As shown in FIG. 3, slots 130 a to 130 e are aligned sequentially along the longitudinal axis of the stringer, and each of the slots has a predetermined distance from a midpoint of the longitudinal axis. The long axis of the elongated slots is preferably either on, or in parallel with, the longitudinal axis, depending on the location of a slot and the desired flex pattern. The location of a slot, as may be expressed by the distance of the slot from the midpoint of the longitudinal axis, can be determined depending on desired flex patterns of a surfboard. It is noted that the location of a slot can also be expressed using other reference points, such as the front end, or the rear end.

FIG. 3 illustrates an example embodiment of a stringer 100 for a shortboard, where the stringer has a length about 6 feet 4 inches, a width about ⅛ inch, a maximum height around the midpoint of the longitudinal axis of about 2 and ⅝ inches and the height near the front and rear ends, at about 12 inches from the ends, is about 1 and 9/16 inches and about 1 and 15/16 inches, respectively. In a typical surfboard, the core body around the midpoint of the longitudinal axis is thickest, because this portion of the entire board experiences the strongest force during surfing. Moreover, the surfer's front foot is also positioned at this portion of the board, which naturally causes a certain degree of flex at this location by the force asserted by the surfer. Therefore, preferably as shown in FIG. 3, no slot, or a slot of very small size, is provided about the midpoint M of the stringer.

In the embodiment shown in FIG. 3, three elongated slots, 130 a-130 c, are placed between the front end 112 and the midpoint M, referred to as the front half, and two elongated slots, 130 d-130 e, are placed between the midpoint M and the rear end 114, referred to as the rear half. The five slots have a length from about 3 inches to about 5½ inches, and a height from about 3/16 to about ⅜ inch. Near the rear end 114, no slot is provided, because typically fin(s) are provided near the tail end of the surfboard, which asserts physical stress and rigidity in this region. As such, slot 130 e is made relatively shorter than 130 d to maintain the strength of the stringer body near a stressful surrounding. However, as can be appreciated, if a water sports board does not have fins at its tail end, slots can be placed in this region to increase flexion at the rear end of the stringer.

In the front half, slot 130 b is the longest among all slots to provide a greater flex in this region. It is known that this region of a surfboard experiences the largest degree of curvature changes along the longitudinal axis of the surfboard during surfing. Elongated slot 130 b enhances the flexibility of the surfboard at this critical region and enables a desired increase of curvature at this region when a water wave is encountered. In combination with slot 130 c near the midpoint M and 130 a near the front end, the front half of the surfboard of the present invention exhibits an increase of overall forward curvature. This increased forward curvature fits better to a smaller (tighter) radius of a wall of water within a wave, therefore, enhances the performance of the surfboard. It is noted that slot 130 a is the smallest in both length and height. Because the height of the stringer body decreases substantially in this region, to maintain the strength of the stringer a small size slot is provided. Moreover, since the surfboard has a smaller dimension in thickness at this region, it requires less pressure to generate a certain degree of flex in comparison to other regions of the surfboard. Therefore, a slot of a smaller size provides sufficient enhancement in the flexibility in the region near the nose end of the surfboard.

FIG. 3 shows an example of a surfboard made using the stringer of the present invention. As can be appreciated, the placement strategy of the slots varies with different water sports boards, depending on the specific structure and configuration of the boards.

In an alternative embodiment, the water sports board of the present invention includes more than one stringer described above. In this embodiment, the water sports board includes two or more elongated planar stringers 100 disposed along the longitudinal centerline of the core body. FIG. 5 illustrates an example of a surfboard 150 that includes two of stringer 100 described above. FIG. 5 shows a top view of a blank of a surfboard, which has inner core 170 and two stringers 100 assembled together, but the outer shell has not be applied. As shown, preferably, two stringers 100 are in a parabolic shape, disposed symmetrically off the longitudinal centerline 2-2′ of core body 160, substantially in parallel with the corresponding side edges 175 a and 175 b of the inner core 170, respectively. The same arrangement can also be applied to a surfboard or other water sports boards that includes four stringers 100. Alternatively, two stringers may be in parallel with the longitudinal centerline of core body 160. When three stringers are used in one board, one stringer can be disposed on the longitudinal centerline of the core body, and two stringers can be positioned apart from and symmetrically off the longitudinal centerline as shown in FIG. 5. In this embodiment, the two or more stringers 100 may have a same or different slot arrangement, depending on the needs.

It is important to understand that multiple parameters of the slots of stringer 100 can be determined or adjusted to achieve a desired or selected flex pattern of a surfboard or other water sports board described above. These include, but not limited to, shape, size particularly length and height, location, orientation, and number of the slots. By providing one or more slots on the stringer body with predetermined or selected parameters described above, the flex pattern of a resulted water sports board containing such a stringer can be controlled, or adjusted to desired characteristics, which ultimately enhances performance of the board. As discussed previously, existing surfboards exhibit random, not pre-determined, and uncontrolled flex patterns and characteristics, which are attributed to the random flex characteristics and resistance to flexing of the solid body stringer. As can be appreciated, multiple controllable or adjustable parameters of the stringer of the present invention in design and placement of the slots provide an unprecedented adjustability to the manufacturers and an unprecedented range of selections to the end users.

The enhancement in property, function and performance of the water sports boards of the present invention can be appreciated from several aspects. First, by placing multiple slots along the longitudinal axis of the stringer, the stringer body is more flexible than a solid planar body. This enhanced flexibility in the stringer, which is the backbone of surfboard or other boards, exhibits in an overall flexibility enhancement of the board. The effect of flexibility enhancement is directly reflected by an increased curvature of the surfboard. FIG. 6 illustrates the original curvature (solid lines) of surfboard 10 in reference to a horizontal plane 3, which commonly referred to as rocker in surfing, and the effect of increased rocker (broken lines) of the surfboard when it experiences forces asserted by the water waves. As observed, the overall rocker of the surfboard of the present invention is substantially enhanced than that of the existing surfboards.

Second, as discussed above, the surfboard of the present invention has an increased forward curvature when encountering water waves and this increased forward curvature fits better to smaller radius of walls of the wave, which facilitates the surfer in performing certain maneuvers such as sharp and hard turns on the bottom or top of a wave.

Third, the increase in surfboard's rocker through flexing also benefits the rider, because of an increase in the spring loading effect within the stringer body. After flexing, the stringer springs back to its original, relaxed shape, which creates an increase in pressure between the bottom surface of the surfboard and the surface of water. This pressure produces a lift, which results in an increase in the speed of the surfboard on the water surface. A repetitive rhythmic action by the surfer utilizing a flexing and springing back technique increases the speed of the surfboard. This action is very desirable in many instances of surfing. As can be appreciated, the increased rocker of the surfboard of the present invention ultimately results in an increase in the lift and the speed of the surfboard. Moreover, the increased flexing also reduces or eliminates a loss of existing speed (bogging) while the surfer performs specific maneuvers, for example, a 180 degree turn.

Fourth, it has also been found surprisingly that the surfboard of the present invention exhibits an unexpected superior shock dampening property, which can be attributed to the enhanced flexibility of the board and the compressibility of the stringer. The shock load that is forced on to a surfboard by a wave crashing onto a surface of the board accounts for a high percentage of board breakage. Because of the unique structure of the slotted stringer, the surfboard of the present invention has desired longitudinal and torsional flexion, which allows the board to resume its original form after the forces are withdrawn, even under harsh conditions and repeated use. In numerous performance tests, the surfboard of the present invention not only outperformed existing surfboards in surfing performance, it also demonstrated an unexpected durability. In one surfer's tests under extreme harsh wave conditions, the life time of the surfboard of the present invention was more than 5 times of the average life time of existing surfboards used under the same conditions.

Fifth, as described above, the flex patterns and characteristics of a surfboard or other water sports boards can be adjusted or controlled by selecting appropriate parameters for the slots. For example, a design can be made to specifically enhance front rocker, but not the rear rocker of a board by providing the slots only in the front half of the stringer, or vice versa. This provides a convenient and wide range of adjustability in designing surfboards or other water sports boards.

In a further embodiment, the present invention provides a method of producing a water sports board using the stringer described above. Stringer 100 can be made of wood, plywood, carbon fiber, fiberglass, polyvinyl chloride (PVC), rubber, para-aramid synthetic fiber, or a combination thereof. Wood and plywood are most common materials used for stringers of surfboards. When plywood is used, at least 2-ply, preferably 3-ply or more, plywood is used.

A stringer 100 is first produced using methods known in the art, to the longitudinal profile of a water sports board to be made. Predetermined size, shape, number and location of the slots are fabricated on the stringer body, by removing the material within a slot to produce a through-opening, or alternatively partially removing the material within a slot to produce a recess on the side surfaces. The ends of slots are smoothed to avoid sharp edges. Alternatively, when the stringer is made of synthetic materials described above, the stringer and the slots can be produced together by plastic molding, or other known methods.

Inner core 40 made of any flotation-type foam material, which includes, but not limited to, extruded polystyrene foam, expanded polystyrene foam beads, polyurethane foam, rigid polyvinylchloride foam, or similar material having light weight and low density.

The inner core can be made using known construction methods. For example, for low volume production the water sports board 10 may be fabricated manually. For a surfboard shown in FIG. 2, two half cores are adhered to the two side surfaces of stringer 100 by an adhesive known in the art to form a blank. Then, the blank is shaped by hand, or machine to the desired shape. Subsequently, a composite skin can be applied and cured using known techniques to form outer shell 30. The composite skin is typically fabricated from a resin/fiber matrix. Appropriate resins include epoxies, polyesters, vinylesters, or other semi-rigid plastics. Fibers to complete the composite may include glass, carbon, boron carbides beryllium, polymerics, or other high strength material having a woven or unidirectional form. The outer shell may be further laminated with a low-frictional thermoplastic polymer film material or other low-friction materials known in the art.

Alternatively, core body 20 can also be hollow produced using techniques known in the art. Here, outer shell 30 is formed along the two side surfaces of stringer 100, or enclosing the top and bottom edges of stringer 100, by molding. In either case, as the backbone of a water sports board, the enhanced flexibility of stringer 100 affords the water sports board 10 enhanced flexion, controllable flex patterns, and durability.

It is noted that all the above described embodiments can be fitted with fins, fin boxes and mast steps or tracks to facilitate the board's use in water sports. Typically, fins, fin boxes and mast steps or tracks are affixed onto or into the outer shell.

While the present invention has been described in detail and pictorially shown in the accompanying drawings, these should not be construed as limitations on the scope of the present invention, but rather as an exemplification of preferred embodiments thereof. It will be apparent, however, that various modifications and changes can be made within the spirit and the scope of this invention as described in the above specification and defined in the appended claims and their legal equivalents. 

1. A water sports board having enhanced flexibility, comprising: (a) an elongated core body having a nose end and a tail end, and top and bottom surfaces defining a curved shape of said water sports board; and (b) an elongated planar stringer having a front end and a rear end, two side surfaces, and top and bottom edges curved to a longitudinal profile of said water sports board, and including multiple slots on said side surfaces disposed between said front and rear ends of said stringer; said planar stringer being disposed on a longitudinal centerline of said core body.
 2. The water sports board of claim 1, wherein said elongated core body includes two symmetrical halves, each secured to one of said side surfaces of said planar stringer.
 3. The water sports board of claim 1, wherein said multiple slots are openings through the width of said stringer.
 4. The water sports board of claim 1, wherein said multiple slots are in a form of recess on said side surfaces partially through the width of said stringer.
 5. The water sports board of claim 1, wherein said multiple slots are disposed along a longitudinal axis of said stringer.
 6. The water sports board of claim 5, wherein said multiple slots are elongated in a direction of said longitudinal axis.
 7. The water sports board of claim 6, wherein said multiple slots have a length from about 2 inches to about 10 inches.
 8. The water sports board of claim 6, wherein said multiple slots have a height from about 1/12 to about ½ of the height of said stringer.
 9. The water sports board of claim 6, wherein a total length of said multiple slots are from about 15% to about 60% of the length of said stringer.
 10. The water sports board of claim 6, wherein said multiple slots have different lengths.
 11. The water sports board of claim 6, wherein said multiple slots are aligned sequentially along said longitudinal axis, each of said multiple slots having a predetermined distance from a midpoint of said longitudinal axis of said stringer.
 12. The water sports board of claim 1, wherein said stringer is made of at least one material comprising wood, plywood, carbon fiber, para-aramid synthetic fiber, fiberglass, polyvinyl chloride (PVC), rubber, or a combination thereof.
 13. The water sports board of claim 1, wherein said stringer has a height substantially same as the height of said core body.
 14. The water sports board of claim 1, wherein said core body comprises an outer shell adhering to and covering top and bottom surfaces of an inner core and said top and bottom edges of said stringer.
 15. The water sports board of claim 1, wherein said water sports board comprises surfboards, windsurf boards, kiteboards, wakeboards, wake skates, or body boards.
 16. A water sports board having enhanced flexibility, comprising: (a) an elongated core body having a nose end and a tail end, and top and bottom surfaces defining a curved shape of said water sports board; and (b) two or more elongated planar stringers, each of said stringers having a front end and a rear end, two side surfaces, and top and bottom edges curved to a longitudinal profile of said water sports board, and including multiple elongated slots on said side surfaces, each of said elongated slots disposed along a longitudinal axis of said stringer with a predetermined distance from a midpoint of said longitudinal axis; said two or more planar stringers being disposed along, and symmetrically off, a longitudinal centerline of said core body.
 17. A stringer of a water sports board having enhanced flexibility, said stringer comprising an elongated planar panel having a front end and a rear end, two side surfaces, and top and bottom edges curved to a longitudinal profile of a water sports board, and multiple elongated slots on said side surfaces; each of said multiple elongated slots disposed along a longitudinal axis of said stringer with a predetermined distance from a midpoint of said longitudinal axis.
 18. The water sports board of claim 17, wherein said multiple slots are elongated in a direction of said longitudinal axis having a length from about 2 inches to about 10 inches.
 19. The water sports board of claim 18, wherein said multiple slots are openings through the width of said stringer.
 20. The water sports board of claim 17, wherein said stringer is made of at least one material comprising wood, plywood, carbon fiber, para-aramid synthetic fiber, fiberglass, polyvinyl chloride (PVC), rubber, or a combination thereof. 